Method and apparatus for vaporizing liquefied gases and obtaining power



F. E. GILMORE Jan. 30, 1962 3 018 634 METHOD AND APPARATUS FOR VAPORIZING LIQUEEIED GASES AND OBTAINING POWER 2 Sheets-Sheet 1 Filed April ll, 1958 n Asili,

INVENTOR. F. E. GILMORE .vIU DBG...-

Jan. 30, 1962 F, E, GlLMoRE 3,018,634

METHOD AND APPARATUS FOR VAPORIZING LIQUEF'IED l GASES AND OBTAINING POWER Flled Aprll 11, 1958 2 Sheets-Sheet 2 iw@ o o w A TTORNEVS United States Patent O 3,018,634 METHOD AND APPARATUS FOR VAPORIZING LIQUEFIED GASES AND OBTAINING POWER Forrest E. Gilmore, Independence, Kans., assignor t Phillips Petroleum Company, a corporation of Dela- Ware Filed Apr. 11, 1958, Ser. No. 727,870 11 Claims. (Cl. 62-52) This invention relates to an improved method and/or apparatus for the vaporization of liquefied gases such as liquefied natural gases, especially methane, and to the recovery and utilization of the refrigeration and power obtainable during said vaporization. In accordance with one aspect, the present invention relates to method and arrangement orf apparatus for vaporizing liquefied gases comprising the step-wise heating and vaporization of said gas in a cascade process wherein said gas is subjected to Warming -in a plurality of successive steps at `substantially a constant pressure. In accordance with another aspect, the present invention relates to method and arrangement of apparatus for vaporizing liquefied gases such as natural gases comprising the step-wise heating and vaporization of said liquefied gas in a cascade process wherein said liquefied gas is subjected to warming at a high pressure, expansion, and further warming in a plurality of successive steps. In accordance with another aspect, this invention relates to method and arrangement `of apparatusv for vaporizing liquefied gases comprising indirectly heating said liquefied gas in a plurality of vaporization zones with heat exchange fluids being continuously circulated in closed refrigeration circuits arranged in cascade relation, said circuits being adapted to also recover the refrigeration and power obtainable during said vaporization. Various methods for liquefying gases such as natural gases, principally methane, and the like, have either been proposed or used. Recently, a considerable amount of interest has developed in the transportation of liquefied natural gases, especially methane, by barge or the like from a producing field, for example, the Gulf Coast area, to a place of utilization of said liquefied gas which is located a substantial distance from the p-roducing field. In order to make the transportation of liquefied natural gases more attractive and feasible economically, it is desirable to recover as much refrigeration as possible during the regasifying of said gas at the place of utilization. Further, at the delivery point or place of utilization of the liquefied gas, the liquefied gas must be vaporized and warmed before use. Vaporizing liquefied natural gases after transporting or storing them at atmospheric pressure is not a simple matter. If part of the liquefied gas is burned to supply all of the heat required to vaporize the gas, almost forty percent of the gas is required as fuel. Further, it is impractical to heat the liquefied gas with air by means of air-fin coolers, for example, because of the heavy frost formed during the heating steps. Thus, it can be -seen that there is a distinct need for a practical and economical method and/or apparatus for vaporizing the liquefied gas at the place of utilization and also to recover and utilize the available refrigeration and power obtainable during the vaporization process without encountering the problems lassociated with the prior art methods of vaporizing liquefied gases. Accordngly, the problems discussed above that are associated with the prior art methods of Vaporizingliquefied gases are obviated by the practice of the present invention.

Accordingly, an object of this invention is to provide a cascade process for the vaporization of liquefied gases. Another lobject of the present invention is to provide an apparatus in cascade relation for vaporizing liquefied gases. Another object of the present invention is to provide an economical and practical method for vaporizing liquefied gases. Another object of the present invention is to provide method and apparatus for utilizing the refrigeration obtainable from the evaporation of liquefied gases in the operation of gas driven turbines. Still another object of this invention s to provide an economical and practical method of obtaining power from liquefied gases vaporized under high pressure and utiliziing the refrigeration so obtained to cool process equipment in processing plants such as refineries and chemical plants. Other aspects, objects, as well as the several advantages of this invention are apparent from the study of the disclosure, the drawings, and the appended claims.

In accordance with the present invention, I provide an improved method of vaporizing liquefied gases such as liquefied natural gases, especially methane, comprising the step-wise heating and vaporization of said gas in a cascade process wherein said gas is subjected to warming at substantially the same pressure at which said gas was maintained as a liquefied gas in a plurality of successive warming or vaporization zones, said zones being indirectly heated by heat exchange fluids that are cycled in systems adapted to also recover and utilize refrigeration and power obtainable in this method.

Also in accordance with the present invention, I provide an improved method of vaporizing liquefied gases such as liquefied natural gases, especially methane, comprising the step-wise heating and vaporization of said gas in a cascade process wherein a stream of said liquefied gas is subjected to warming at a pressure substantially higher than the pressure which said liquefied gas was maintained as a liquefied gas, expansion, and further warming in a plurality of successive zones, said zones being adapted to recover and utilize the refrigeration and power obtainable in the method.

Further in accordance with the present invention, I provide an apparatus for the vaporization of liquefied gases comprising, in combination, a plurality of vaporization means, a plurality of heat exchange fiuid circuits for heating said vaporization means, each circuit being adapted to recover and utilize the refrigeration and energy obtainable during said vaporization. Additionally, I provide an apparatus comprising, in combination, vaporization means, pressure expansion means, and heat exchange means, said vaporization and heat exchange means being heated lby a heat exchange uid cycled -in a closed circuit also adapted to utilize the refrigeration obtained by said fluid.

ln accordance with one specific embodiment of the present invention, I provide an improved method for vaporizing liquefied gases such as liquefied natural gases, especially methane, by indirect heat exchange andto the recovery and utilization of the refrigeration and power obtainable in the method comprising raising the temperature of said gas gradually and step-wise at substantially a constant pressure by subjecting a continuous stream of said liquefied gas to warming in a plurality of indirect heat exchange or vaporization zones, at least a portion of said liquefied gas being vaporized in each of said zones, said vaporization zones being heated with heat exchange fluids being continuously cycled in a plurality of closed refrigeration circuits arranged in cascade relation and wherein said heat exchange fluids have a change of state by heat interchange with said liquefied gas in said vaporization zones, each of said refrigeration circuits comprising a pumping zone for compression and circulation of its heat exchange fluid, a plurality of indirect heat exchange zones adapted to recover and utilize the refrigeration obtained by said heat interchange, a pressure reducing zone adapted to utilize the kinetic energy released in said pressure reduction zone as a source of power, said vaporization zones for heat interchange between said liquefied gas and said heat exchange fluids so as to cause said liquefied gas to be heated and vaporized and said heat exchange fiuids to be condensed, and recovering as a product of the process said liquefied gas as a gas.

In accordance with another embodiment of the present invention, I provide an improved method for vaporizing liquefied gases such as liquefied natural gases, especially methane, that have been transported a substantial distance and stored as a liquefied gas at a low temperature and at substantially atmospheric pressure and for the recovery and utilization of the refrigeration and power obtainable during said vaporization process comprising the steps of substantially increasing the pressure of a stream of said liquefied gas without substantially changing the temperature of said liquefied gas, vaporizing said liquefied gas of increased pressure by subjecting said stream of said liquefied gas to warming in a vaporization zone by indirect heat exchange with heat exchange fluid being continuously cycled through a closed system, recovering the refrigeration released by the evaporation of said liquefied gas in said vaporization zone by utilizing said heat exchange fiuid of reduced temperature as a cooling medium in a chemical processing plant or zone, for example, substantially reducing Ithe pressure of the evaporated liquefied gas in a pressure reduction zone adapted to utilize the kinetic energy released in said zone as a source of power, subjecting the evaporated liquefied gas of reduced pressure and temperature to direct heat exchange with said heat exchange uid in a second heat exchange zone to recover additional refrigeration, and'recovering as a product of the process said liquefied gas as a gas.

Thel present invention is applicable to the vaporization of any liquefied gas wherein it is desired to recover' and utilize the refrigeration and power obtainable during the vaporization of said gas. The present invention is particularly applicable for the vaporization of a liquefied natural gas, principally methane, that has been liquefied near the producing field for example, by compression and cooling to about -250 to about -260 F., and then expanded to atmospheric pressure before transportation, and then transported by barge, tanker, and the like at atmospheric pressure at about 260 F. to a place of utilization, which is located a substantial distance from the liquefaction plant, and at the place of utilization said gas is vaporized and the refrigeration and power obtainable during the vaporization of the gas is recovered and utilized. The liquefied gas can first be stored before vaporization or it can be vaporized as it is unloaded from the conveying means. Y

The refrigeration recovered by the practice of the vpresent invention during the vaporization of said liquefied gas can be'conveniently used for example, to refrigerate frozen food plants, meat packing houses, dewaxing operations in petroleum refineries, air conditioning in offices and buildings, cooling process equipment in chemical plants, and the like. The pressure expansion zones ernployed in the practice of the present invention such as expansion engines, turbine zones, and the like, are preferably adapted to utilize the kinetic energy in the expansion zone as a source of power for driving pumps, compressors, electric generators, and the like.

It is a feature of this invention that, in a method for the vaporization of liquefied gases, such as liquefied natural gases, principally methane, the liquefied gas is heated in a plurality of vaporization zones by indirect heat exchange with a plurality of refrigerants being continuously cycled in a plurality of refrigerant circuits in cascade relation and wherein the refrigerants of said circuits have a change of state by heat interchange between said refrigerantsrand said liquefied gas. It is also a feature of the present invention that each of the refrigerant circuits preferably have one or more indirect heat exchange zones with brine for example, to recover therefrgeration obtainable in the evaporation of said liquefied gas. It is also a feature of this invention that each of the refrigerant circuits preferably have a pressure reduction or turbine zone wherein the refrigerant is expanded to develop power and the exhaust gases from said turbine zone are condensed by heat interchange with said liquefied gas in the vaporization zones thereby obtaining power from low level heat sources. Thus, in effect, in one embodiment the warm expanded refrigerant is utilized in warming the liquefied gas to be vaporized. It is another feature of the present invention, as set forth in the second embodiment described above, that a warmed heat exchange fluid or coolant is utilized in warming and Vaporizing the liquefied gas at a high pressure prior to the expansion of the heated vapors of said liquefied gas to obtain power therefrom. Other features of the present invention will become apparent to those skilled in the art upon reading the description of the accompanying drawings.

Further objects and the advantages of the inveniton will be apparent from the following description taken in connection with the accompanying drawings wherein:

`FIGURE l is a simplified diagrammatic flow sheet for vaporizing liquefied methane wherein two adjacent refrigeration circuits in cascade relation are utilized to heat the liquefied gas.

FIGURE 2 is a simplified diagrammatic fiow sheet which illustrates a similar method for vaporizing lique fied methane wherein said liquefied gas is vaporized under high pressure and the heated high pressure vapors of said gas are expanded through a turbine to develop power.

Referring now to FIGURE 1, which illustrates one application of my invention utilizing liquefied methane as a liquefied gas to be vaporized. Liquefied methane from a source, not shown, is passed by way of conduit 10 and -introduced into evaporator or vaporization zone 11, wherein said liquefied methane is heated by indirect heat exchange by ya refrigerant being cycled in a closed circuit to be described hereinafter. The vaporized liquefied methane of increased temperature is removed from evaporator 11 by way of conduit 12 and introduced into second heat exchange or vaporization zone 13 wherein the vaporized liquefied gas is subjected to heating by indirect heat exchange with propane which is utilized as a refrigerant being circuated in a second refrigerant circuit, also to be described hereinafter. A stream of methane which is completely vaporized is removed from heat exchange zone 13 by way of conduit 14 and introduced into a brine chiller 15 wherein the methane is further warmed by indirect heat exchange with a brine which is utilized elsewhere as a source of refrigeration. Methane is then removed from chiller 15 and passed through air-fin cooler 16 which recovers additional refrigeration and further warms the vaporized methane which is removed as a gas from air-fin cooler 16 by way of conduit 17 and passed to a pipeline for example, to market'or a place of utilization.

Liquefied methane, as described above, is heatedl in evaporator 11 by indirect heat exchange with ethane gas introduced by way of conduit 18 into evaporator 11, the ethane gas being circulated continuously in a closed refrigerant circuit. In evaporator 11 the ethane refrigerant is condensed by heat interchange with the liquefied methane and liquid ethane is removed from evaporator 11 by way of conduit 19 and introduced into pump 20. The ethane refrigerant circuit includes pump zone 20, ethane evaporator 22, brine chiller 24, air-fin cooler 26, and pressure reduction or turbine zone 28.

In the ethane circuit, the ethane leaves turbine zone 28 as avgas at low pressure through conduit 18 and is introduced into evaporator 11 wherein the ethane gas is condensed and is removed by conduit 19 asv liquid ethane and introduced intorpump 20.` Pump 20 raises the pressure of the liquid ethane and aids inthe circulation of the liquid ethane through the refrigeration circuit and is then passed by way of conduit 21 and introduced into ethane evaporator 22 wherein the ethane is heated by indirect heat exchange with a portion of the gaseous refrigerant being circulated in the second refrigerant circuit. Warmed ethane vapors are removed from evaporator 22 and passed by way of conduit 23 to brine chiller 24 wherein the ethane vapors are further heated by indirect heat exchange with a brine which is used as a source of refrigeration elsewhere. The further warmed ethane vapors are removed from chiller 24 by line 25 and introduced into air-fin cooler 26 which is utilized as a source of refrigeration for air conditioning. The heated ethane vapors removed by conduit 27 from air-fin cooler 26 are introduced into pressure reduction or turbine zone 28 which is adapted to utilize the kinetic energy released in the turbine zone as a source of power. The heated ethane vapors exhausted from turbine zone 28 are then condensed by heat interchange with liquefied methane as described above.

Heat exchange zone 13, as mentioned above, is served by a propane circuit whereby the propane acts as a heat exchange fiuid to warm the vaporized methane in heat exchanger 13. The propane refrigeration circuit includes pump zone 30, brine chiller 31, air-fin cooler 33, turbine or expansion engine zone 35, and ethane evaporator zone 22 and propane condenser zone 13.

In this circuit, the propane leaves turbine or expansion engine zone 35 as a gas and is removed from said zone by way of conduit 36, and a portion of the propane gas is passed to ethane evaporator 22 for heat interchange with the refrigerant of the first refrigerant circuit. The remainder of the propane gas removed from turbine zone 35 is passed by way of conduit 38 and introduced into 'propane condenser or heat exchange zone 13 wherein the warm propane is utilized to heat the vaporized methane passing through heat exchange zone 13 and also'to condense propane gas. Liquefied propane removed from ethane evaporator 22 by way of conduit 39 and propane condenser 13 by way of conduit 29 is introduced into pump zone 30 wherein the pressure of the cold liquid propane is raised. The liquid propane removed from pump zone 30 is passed to brine chiller 31 wherein the propane is vaporized and heated by indirect heat exchange with a brine which is used as a refrigerating agent elsewhere. Warm vaporized propane is removed from chiller 31 by way of conduit 32 and introduced into air-fin cooler 33 wherein the propane gas is further warmed by heat interchange with air. The air can be utilized as a source of air conditioning. Warm propane is then removed from air-fin cooler 33 by line 34 and introduced into expansion engine or turbine zone 35 wherein the pressure of the propane gas is reduced. Expansion engine or turbine zone 3S is adapted to supply the kinetic energy released in the zone as a source of power to drive a pump, generator, etc., not shown. The propane exhaust gases removed zone 35 are condensed by heat interchange with either the refrigerant in the first refrigerant cycle or the liquid methane beingvaporized.

' The refrigerants used in the cascade refrigeration circuits discussed above may vary considerably in characteristics, depending on the conditions under which it is produced and the temperatures and pressures utilized in the particular refrigerant circuits; refrigerants may consist of ethane, propane, or butane, or a mixture of these materials, and may also contain appreciable amounts of methane, ethylene, and similar hydrocarbon materials. Although I have shown the use of brine being passed through the chillers described above it should be realized that other fluids can be passed through the chiller such as butane, for example, which could be used to drive additional turbines. Also, any kind of an expansion engine which is adapted to develop useful work can be used in place of the turbines described above. Further, where the brine chiller is used in the methods described above, if there is no useful refrigeration to be accomplished, the brine can usually be heated by exchange with the atmosphere through air-tin coolers, for example. Usually, the brine can be used to produce water ice, the temperatures indicated hereinafter being right for this use.

Referring now to FIGURE 2 which illustrates a somewhat difierent method of liquefying natural gas, pure methane being used for illustrating the method, where inexpensive power can be produced. In the practice of this method, the gas vaporization can be conveniently accomplished in conjunction with some oil refinery or chemical plant, for example, where useful cooling can be obtained indirectly from evaporating the liquefied gas, methane in the present instance.

Liquefied methane under atmospheric pressure stored in tank 39 is removed by way of conduit 40 and passed to pump zone 41 wherein the pressure of said liquefied methane is appreciably increased. Cold, high pressure liquefied methane is passed by way of conduit 42 to heat exchange or gasifying zones 43 wherein the methane is vaporized and heated by indirect heat exchange with a low freezing heat exchange fluid such as normal pentane, which heat exchange iinid is circulated continuously in a closed system and is employed as a cooling medium for overhead condensers of fractionators of an oil refinery and/or a chemical plant, for example.

The closed circuit emplcyed for circulating a low freezing heat exchange iluid includes surge tank 49, circulating pump zone 53, heat exchanger gasifying zones 43 and 47, heat exchanger condenser zone 59, and the inter-connecting piping.

The heat exchange fluid is circulated through the circuit by pump 53 and passed through conduit 54, and a portion of the pump discharge is passed by way of line 55 through heat exchange zone 47 to indirectly heat expanded methane vapors to be described hereinafter. The remaining portion of the heat exchange iiuid is passed by way of conduit 56 .through heat exchange or gasifying zone 43 wherein the liquefied methane under pressure is vaporized by indirect heat exchange with said heat exchange fluid The cooled heat exchange fluid removed from heat exchange zones 43 and 47 through conduits 57 and 52, respectively, are passed by way of conduit 58 and introduced into heat exchanger condenser zone 59 which i's employed to condense the overhead vapors removed from a fractionator 62 by way of conduit 61. The condensed vapors removed overhead from fractionator 62 are passed to accumulator 63 for use as recycle or as product as desired. The warmed heat exchange fluid is removed from condenser 59 by way of conduit 60 and returned to pump 53 for circulation again through the closed system. Make-up heat exchange fluid can be added by way of conduit 50 into the circuit from surge tank 49.

Warmed methane gas removed from heat exchange or gasifying zones 43 by way of conduit 44 is introduced into expansion engine or gas turbine zone 45. Zone 45 is adapted to supply the kinetic energy released in the turbine zone as a source of power to drive pumps, generators, and the like. Cold exhaust methane gas removed by conduit 46 from expansion zone 45 is further warmed by indirect heat exchange with the heat exchange uid previously described in heat exchange zone 47 to recover additional refrigeration. Warm, low pressure methane gas is removed by way of conduit 48 as a product of the method and can be delivered or transported to a place of utilization.

Although I have used fractionators in an oil refinery or a chemical plant as a source of heat from the atmosphere, it should be realized that other means such as aircoolers and the like can be used in the method described in FIGURE 2.

As an example of a specific operation in accordance with FIGURE l of the present invention, 107,000,000 standard cubic feet per day of liquefied methane at a temperature of 242 F. and at a pressure of 32 p.s.i.a. is passed to evaporator 11. The liquid methane is heated and evaporated in evaporator 11 which condenses ethane gas exhausted from turbine 28 at less than l p.s.i.a., the evaporating temperature being about -240 F. at 30 p.s.i.a. The condensed ethane is pumped to ethane evaporator 22, and the vapors then passing in succession through brine chiller 24, air-fin cooler 26, and the brine chiller heating the ethane gas from 50 F. to -10 F. and the air-fin cooler further heating it to 40 F., at which temperature it enters turbines 28 at a pressure of 80 p.s.i.a. Assuming 90 percent of the heat reduction in the gas is converted to useful work, 4,730 kw. is obtainable.

Ethane evaporator 22 is heated by the `condensation of propane gas exhausting f'om turbine 35 and the 240 F. methane gas removed from evaporator 11 is also used to condense propane gas` exhausted from turbine 35 in condenser 13, the methane gas being thereby heated to 50 F. Methane gas is further heated in brine chiller 1S to about 10 F., and then to about 40 F. by means of air-fin cooler 16 before delivering methane gas by way of conduit 17 to a place of utilization.

The propane gas condensed in ethane evaporator Z2 and propane condenser 13 at 50 F. is pumped through brine chiller 31 wherein it is vaporized and heated to about F., and then passes through air-fin cooler 33 wherein it is heated to about 40 F., at which temperature and at about 30 p.s.i.a. propane gas enters turbine 35 as its driving fluid. About 1,175 kw. of power is recovered in turbine 35 making the total power recovered about 5,900 kw.

Approximately 272 tons of refrigeration are recovered in chiller 24, approximately 359 tons are recovered in airfin cooler 26, approximately 5,640 tons in chiller 31, approximately 468 tons in air-fin cooler 33, approximately 343 tons in chiller 15, and approximately 390 tons of refrigeration are recoveredV in air-fin cooler 16. Thus, the total amount of refrigeration recovered is approximately 7,500 tons. Thus, it can be seen that a substantial amount of refrigeration and power is obtainable by the practice of the present invention.

As an example of a specific operation in accordance with the embodiment described in FIGURE 2 of the present invention, 107,000,000 standard cubic feet per day of 260 F. liquid methane stored at 14.7 p.s.i. pressure is removed from a storage tank and the pressure increased to 610 p.s.i.a. The high p'essure methane is vaporized in gasifiers 43 wherein the temperature of the methane is raised to about 70 F. and the pressure of the methane gas is approximately 600 p.s.i.a. The heated methane vapors are expanded through a gas turbine wherein about 4,850 kw. of power is recovered and the cold exhaust gas is removed from turbine 45 at a temperature of about -167 F. and at 60 p.s.i.a. and is passed to heat exchangers 47 wherein the methane gas is warmed to about 20 F. and 55 p.s.i.a. for passage to a place of utilization. In addition to the power recoverable by turbine 45, approximately 84,000 M B.t.u. per hour duty heat exchanger or condenser such as condenser 59 in FIGURE 2 can be cooled by normal pentane, for example, circulated in the closed system illustrated.

As can be seen from the above example, I have provided a practical and economical method of utilizing the refrigeration obtainable from the evaporation of liquefied natural gas such as methane in the operation of gas driven turbines yto condense the turbine exhaust gases and thereby obtaining power from low level heat sources such as the atmosphere, and also a similar method, as described in FIGUREV 2, of obtaining power by expanding through a turbine the heated vapors from liquefied natural gas such as methane, vaporized under high pressure and using the refrigeration so obtained to cool the overhead condensers, for example, of a fractionator in an oil renery or chemical plant.

Reasonable.l variation and modification are possible within the scope of the foregoing disclosure, the drawings, and the appended claims to the invention, the essence of which is that there have been disclosed methods and/or apparatus for vaporizing liquefied gases such as liquefied natural gases, especially methane, comprising in one embodiment, subjecting a continuous stream of said liquefied gas to heating in a plurality of heat exchange or vaporization zones, said heat exchange zones being heated by a plurality of refrigerant circuits arranged in cascade relation wherein the refrigerants of said circuits have a change of state by heat interchange between said refrigerants and said liquefied gas, each refrigerant circuit having a pumping zone for compression and circulation of its refrigerant, indirect heat exchange zones for recovering refrigeration, and pressure expansion or turbine zones adapted to utilize the kinetic energy released as a source of power, thereby obtaining power from a low level heat source such as the atmosphere; and a similar method of obtaining power by expanding through a pressure reduction or turbine zone the heated vapors from liquefied gas such as liquefied natural gas vaporized under high pressure, and using the refrigeration so obtained to cool processing equipment, for example, of a chemical plant.

I claim:

l. A method of vaporizing a liquefied natural gas comprising subjecting a stream of said liquefied gas to heating in a plurality of successive heat exchange zones arranged in cascade relation and thereby vaporizing said liquefied gas, heating at least one of said exchange zones indirectly with an expanded heat exchange fluid being cycled in a closed heat exchange circuit, said circuit being adapted to recover refrigeration and power obtained by heat interchange between said liquefied gas and said fluid, and recovering as a product of the method said liquefied gas as a gas.

2. A method of vaporizing a liquefied natural gas comprising subjecting a stream of said liquefied gas to heating at substantially the same pressure at which said liquefied gas is maintained in a liquefied state prior to heating in a plurality of successive heat exchange zones arranged in cascade relation and thereby vaporizing said liquefied gas, heating at least one of said heat exchange zones indirectly with an expanded heat exchange fluid being cycled in a closed heat exchange circuit and wherein said heat exchange fluid is condensed by heat interchange with said liquefied gas, said circuit being adapted to recover refrigeration and power obtained during said heat inter-i change between said liquefied gas and said fluid, and recovering as a product of the method said liquefied gas as a gas.

3. Amethod of vaporizing a liquefied natural gas comprising subjecting a lstream of said liquefied gas to heat interchange with a heat exchange fluid warmer than said liquefied gas in a plurality of successive indirect heat exchange zones and thereby vaporizing said liquefied gas, heating at least two of said heat exchange zones with expanded' heat exchange fluids being cycled in adjacent closed heat exchange circuits and wherein said heat exchange fluids in each of said circuits arranged in cascade relation are condensed by heat interchange with said liquefied gas in said heat exchange zones, said circuits being adapted to recover refrigeration and power obtainable during said heat interchange, and recovering as a product of the method said liquefied gas as a gas.

4. A method of vaporizing a liquefied natural gas comprising subjecting a stream of said liquefied natural gas to heating at substantially a constant pressure in a plurality of successive heat exchange zones arranged in cascade relation and thereby vaporizing said liquefied natural gas, cyclically subjecting a first heat exchange fluid comprising a light hydrocarbon to compression, vaporization by indirect heat exchange with a refrigerant, expansion in a pressure reduction or pressure expansion zone adapted to utilize the kinetic` energy released in said zone as a source of power, and condensation by heat interchange with said liquefied natural gas in a first heat exchange zone, cyclically subjecting a second heat exchange fluid comprising a different light hydrocarbon to compression, vaporization by indirect heat exchange with a refrigerant, expansion in a pressure reduction or pressure expansion zone adapted to utilize the kinetic energy released in said zone as a source of power, and condensation by heat interchange with said liquefied natural gas in a second heat exchange zone, further raising the temperature of said liquefied natural gas to a desired temperature for use by indirect heat exchange in the remaining heat exchange zones, and recovering as a product of the method said liquefied gas as a gas.

5. In the art of liquefying a liqueable natural gas and transporting said liquefied natural gas a substantial distance at a very low temperature and substantially at atmospheric pressure to a place of utilization of said liquefied natural gas, and wherein it is desired to recover refrigeration and power obtainable during the evaporation of said gas before utilization at said place, the improvement comprising subjecting a stream of said liquefied natural gas to step-Wise heating at substantially atmospheric pressure in a plurality of heat exchange zones -to vaporize said liquefied natural gas, heating at least two of said heat exchange zones by indirect heat exchange with different expanded heat exchange fluids circulated in adjacent closed heat exchange circuits arranged in cascade relation, and wherein each heat exchange fluid is condensed by heat interchange with said liquefied natural gas in said heat exchange zones, said circuits being further adapted to recover refrigeration and power obtainable during said heat interchange, and recovering as a product of the method said liquefied natural gas as a gas.

6. In the art of liquefiable natural gas and transporting said liquefied natural gas a substantial distance at a very low temperature and substantially at atmospheric pressure to a place of utilization of said liquefied natural gas, and wherein it is desired to recover refrigeration and power obtainable during the evaporation of said gas before utilization at said place, the improvement comprising subjecting a stream of said liquefied natural gas to step-wise heating at substantially atmospheric pressure in a plurality of heat exchange zones to vaporize said liquefied natural gas, heating at least two of said heat exchange zones by indirect heat exchange with different heat exchange fluids circulated in adjacent heat exchange circuits arranged in cascade relation, said heat exchange fluid in each of said circuits being cyclically subjected to compression, indirect heating with a refrigerant to vaporize said heat exchange fluid, expanded in a pressure reduction zone adapted to utilize kinetic energy released in said zone as a source of power, and condensation by heat interchange with said liquefied natural gas in said heat exchange zones, and recovering as a product of the method said liquefied gas as a gas.

7. Apparatus for the vaporization of a liquefied gas and for the recovery and utilization of the refrigeration and energy obtainable during said vaporization comprising, in combination, a plurality of operatively connected vaporization means adapted to heat and vaporize said gas, a plurality of heat exchange fluid circuits in cascade relation for heating said vaporization means, each circuit having pump means, heat exchange means for recovering refrigeration, turbine means adapted to utilize the kinetic energy released in said means as a source of power, and said vaporization means.

8. Apparatus for the vaporization of a liquefied gas and for the recovery and utilization of the refrigeration and energy obtainable during said vaporization comprising, in combination, vaporization means for heating and vaporizing said gas, pressure expansion means for expanding said vaporized gas, said expansion means being adapted to utilize the kinetic energy released in said means as a source of power, and heat exchange means for further heating said expanded gas, said vaporization and said heat exchange means being heated indirectly by a heat exchange fluid cycled in a closed circuit adapted to utilize the refrigeration obtained by said fluid by heat interchange with said gas.

9. In the art of liquefying a liquefiable natural gas and transporting said liquefied natural gas a substantial distance at a very low temperature and substantially at atmospheric pressure to a place of utilization of said liquefied natural gas, and wherein it is desired to recover refrigeration and power obtainable during the evaporation of said gas before utilization at said place, the improvement comprising subjecting a stream of said liquefied natural gas to step-wise heating at substantially atmospheric pressure in a plurality of heat exchange zones to vaporize said liquefied natural gas, heating at least two of said heat exchange zones by indirect heat exchange with heat exchange fluids circulated in adjacent heat exchange circuits arranged in cascade relation, said heat exchange fluid in each of said circuits being cyclically subjected to compression, indirect heating with a refrigerant to vaporize said heat exchange fluid, expanded in a pressure reduction zone adapted to utilize kinetic energy released in said zone as a source of power, and condensation by heat interchange with said liquefied natural gas in said heat exchange zones, and recovering as a product of the method said liquifed gas as a gas.

10. A method according to claim 4 wherein said first heat exchange fluid is ethane and said second heat exchange fluid is propane.

11. In the art of liquefying a liquefiable natural gas and transporting said liquefied natural gas a substantial distance at a very low temperature and substantially at atmospheric pressure to a place of utilization of said liquefied natural gas, and wherein it is desired to recover refrigeration and power obtainable during the evaporation of said gas before utilization at said place, the improvement comprising subjecting a stream of said liquefied natural gas to step-wise heating at substantially atmospheric pressure in a plurality of heat exchange zones to vaporize said liquefied natural gas, heating at least two of said heat exchange zones by indirect heat exchange with heat exchange fluids circulated in adjacent heat exchange circuits arranged in cascade relation, said cascade relation comprising heat exchanging the heat exchange fluids in adjacent heat exchange circuits to transfer heat from the downstream heat exchange circuit to the upstream heat exchange circuit, said heat exchange fluid in each of said circuits being cyclically subjected to compression, indirect heating with a refrigerant to vaporize said heat exchange fluid, expanded in a pressure reduction zone adapted to utilize kinetic energy released in said zone as a source of power, and condensation by heat interchange with said liquefied natural gas in said heat exchange zones, and recovering as a prdouct of the method said liquefied gas as a gas.

References Cited in the file of this patent UNITED STATES PATENTS 2,418,446 Anderson Apr. 8, 1947 2,463,881 Kemler Mar. 8, 1949 2,467,413 Wildhack Apr. 19, 1949 2,484,875 Cooper Oct. 18, 1949 2,586,454 Brandin Feb. 19, 1952 2,658,360 Miller Nov. 10, 1953 2,737,031 Wulle Mar. 6, 1956 2,753,700 Morrison July 10, 1956 2,909,906 Bocquet et al. Oct. 27, 1959 2,937,504 Riediger May 24, 1960 2,964,917 Webster Dec. 20, 1960 FOREIGN PATENTS 736,736 France Sept. 26, 1932 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nm 3o18634 o January 3o 1962 ForrestEo Gilmore v r It is hereby certified that error appears in the above numbered patent requiring correction andvthat the said Letters Patent should read as corrected below.

Column 9v line 36 after ,"of insertV lquefyi'ng a me;

Signed and sealed this 5th day of June I92V (SEAL) Attest:

vERNEST w. swIDER. d DAVID L- LADD Atteting Officer v t Commissioner of Patents 

3. A METHOD OF VAPORIZING A LIQUEFIED NATURAL GAS COMPRISING SUBJECTING A STREAM OF SAID LIQUEFIED GAS TO HEAT INTERCHANGE WITH A HEAT EXCHANGE FLUID WARMER THAN SAID LIQUEFIED GAS IN A PLURALITY OF SUCCESSIVE INDIRECT HEAT EXCHANGE ZONES AND THEREBY VAPORIZING SAID LIQUEFIED GAS, HEATING AT LEAST TWO OF SAID HEAT EXCHANGE ZONES WITH EXPANDED HEAT EXCHANGE FLUIDS BEING CYCLED IN ADJACENT CLOSED HEAT EXCHANGE CIRCUITS AND WHEREIN SAID HEAT EXCHANGE FLUIDS IN EACH OF SAID CIRCUITS ARRANGED IN CASCADE RELATION ARE CONDENSED BY HEAT INTERCHANGE WITH SAID LIQUEFIED GAS IN SAID HEAT EXCHANGE ZONES, SAID CIRCUITS BEING ADAPTED TO RECOVER REFRIGERATION AND POWER OBTAINABLE DURING SAID HEAT INTERCHANGE, AND RECOVERING AS A PRODUCT OF THE METHOD SAID LIQUEFIED GAS AS A GAS. 